The present invention relates generally to one-way drive devices and methods of operating such devices and, more specifically, to one-way drive devices in which the engagement impact in the transition from the overrunning mode to the locked mode is reduced.
One-way drive devices join two shafts in such a way that the first shaft drives the second shaft when driven in one direction, but the first shaft disconnects from the second shaft when driven in the opposite direction. An example of a one-way clutch is the type known as a MECHANICAL DIODE® (hereafter referred to as MD) manufactured under license given by Epilogics, Inc. The MD achieves this one-way drive behavior using a high resolution, planar ratchet mechanism. Such a device is disclosed, for instance, in U.S. Pat. No. 5,070,978 issued to Paul B. Pires (hereafter referred to as the Pires patent and incorporated herein by reference).
Turning now to the drawings, wherein like components are indicated by like reference numbers throughout the various figures, attention is immediately directed to FIGS. 1A and 1B, which illustrate the major components of a typical MD of the type disclosed in the Pires patent. FIG. 1A illustrates one face of a pocket plate 10 of an MD mechanism. Pocket plate 10 includes a plurality of indentations 12 for coupling out or in of torque to or from an external shaft (not shown). Pocket plate 10 also includes a plurality of pockets 14, which are configured for housing a plurality of struts 16 therein. Each strut 16 also includes a pair of ears 17 along one edge. Ears 17 are designed to cooperate with a pair of strut locating shoulders 18 of pocket 14 such that strut 16 remains within pocket 14 during the operation of the MD. Another component of a typical MD mechanism is a notch plate 20, illustrated in FIG. 1B, which includes a plurality of notches 22 on one face. When notch plate 20 is positioned in a face-to-face relationship with pocket plate 10 of FIG. 1A, notches 22 are designed cooperate with struts 16 such that one of struts 16 engages one of notches 22 to transfer torque therebetween. It should be noted that torque can be transferred from pocket plate 10 to notch plate 20 via one of struts 16 such that pocket plate 10 drives notch plate 20 or, just as readily, torque can be transferred from notch plate 20 to pocket plate 10 via one of struts 16 such that notch plate 20 drives pocket plate 20.
The details of the operation of the typical MD is further illustrated in FIGS. 2A and 2B, which illustrate partial cross-sectional views of the MD with pocket plate 10 and notch plate 20 arranged in face-to-face relationship. As can be seen in FIGS. 2A and 2B, pocket 14 of pocket plate 10 includes a well 32, which is configured to accommodate a bias spring 32. Bias spring 32 is configured to bias a first edge 34 of strut 16 toward notch plate 20. A second edge 36 of strut 16 is designed such that, as first edge 34 rotates toward notch plate 20, second edge 36 rotates into pocket 14 such that second edge 36 engages a load bearing surface 38 of pocket 14. Each of notches 22 of notch plate 20 includes a slanted surface 40 and a shoulder 42.
The MD in driving mode is shown in FIG. 2A. As can be seen in FIG. 2A, shoulder 42 is configured to cooperate with first edge 34 of strut 16 such that when, for example, notch plate 20 rotates in a driving direction as indicated by arrow 50A, first edge 34 of strut 16 is biased into engagement with shoulder 42. Consequently, torque is transferred from shoulder 42 through first edge 34 and second edge 36 of strut 16 to pocket plate 10 through load bearing surface 38 such that pocket plate 10 is driven in a driven direction indicated by an arrow 52. The direct imposing of strut 16 between notch plate 20 and pocket plate 10 forms a very strong connection between the two plates, thus allowing the transfer of large torques and loads therebetween.
In contrast, the MD in overrunning mode is shown in FIG. 2B. In this case, notch plate 20 rotates in an overrunning direction as indicated by an arrow 50B. Slanted surface 40 of each notch 22 serves to rotate strut 16 toward pocket plate 10 and thus out of engagement with shoulder 42. As a result, notch plate 20 no longer drives pocket plate 10 and the two plates are rotationally disconnected. In other words, in the overrunning mode, pocket plate 10 and notch plate 20 each moves freely with respect to the other plate. Also, ears 17 on strut 16 cooperate with strut locating shoulders to keep strut 16 substantially within pocket 14 during overrunning mode.
Continuing to refer to FIGS. 2A and 2B in conjunction with FIGS. 1A and 1B, one possible problem with the MD type of one-way drive device is a noise or abrupt shock caused during the transition from the overrunning mode to the drive mode. There are thought to be two reasons for the shock or noise present during this operating mode change. The first reason is the positive, surface to surface contact of the strut and plates when in the drive mode, as shown in FIG. 2A. That is, the impact of first edge 34 of strut 16 hitting shoulder 42 of notch plate 20 can result in a noise or shock. A second reason is the angular distance between engagement opportunities (i.e., the angular distance between the opportunities for one of the struts in the pocket plate to engage a shoulder of one of the notches in the notch plate) afforded by the MD design. As most readily seen in FIGS. 1A and 1B, this angular distance can vary from as little as 1-or 2-degrees to as much as 10- to 20-degrees depending on the number and position of struts/pockets and the number of notches used in a specific clutch arrangement. Regardless of this angular distance, the actual reversal of driving direction in the transition from the overrunning mode to the drive mode, if the transition occurs in a random fashion, can occur anywhere within the space between engagement opportunities. On those occasions when the reversal occurs just before an engagement opportunity, i.e., just before a strut is able to engage a shoulder in a notch, the notch plate accelerates in the drive direction from the instant of reversal until the strut becomes fully seated in the previously encountered notch. That is, the notch plate accelerates in the drive direction until the instant of engagement such that, when engagement does occur, the notch plate must be decelerated almost instantaneously to match the speed of the pocket plate or the pocket plate must be almost instantaneously accelerated to match the speed of the notch plate. This very rapid change in speed occurring at the instant of engagement can, under some conditions, be perceived as an audible click or perturbation of the motion of the shafts attached to the MD. This occasional click occurring at the instant of engagement can be especially objectionable when one of the plates of the MD is attached to a stationary drive line element, such as an automotive transmission case.
The present invention provides one-way drive devices which are intended to reduce or eliminate the foregoing problems in a heretofore unseen way and which provides still further advantages.